1. Field of the Invention
The present invention relates to a Bi-MOS circuit which is driven by an MOS circuit and more particularly, to a Bi-MOS levelshift circuit with a high-voltage double-diffused metal oxide semiconductor field effect transistor and a high-voltage bipolar transistor.
2. Description of the Related Art
An integrated circuit for driving an electronic display such as fluorescent display and electroluminescent display includes a data processing section operated at a low power voltage and an output section which drives a display device at a high power voltage. The power voltage in the data processing section is generally 5 V and, in virtue of power saving, a complementary MOS (CMOS) circuit is used therefor. The power voltage in the output section is 40 to 100 V in the case with a fluorescent display and 100 to 250 V in the case with an electroluminescent display. A levelshift circuit is used so as to transmit a signal from the data processing section to the output section.
The present inventor has designed and tested a levelshift circuit having a CMOS inverter connected between a low-voltage power source line and the ground, a PNP bipolar transistor having an emitter connected to a high-voltage power source line and a collector connected to a load, and an N-channel double-diffused MOS transistor having a drain connected to the base of this bipolar transistor, a source connected to the ground, and a gate connected to the output of the CMOS inverter. The double-diffused MOS transistor has a high withstand voltage characteristic and is suitable for being used in the high power voltage circuit. According to the inventor's experimental test, the circuit could normally function as a levelshift circuit, but it was difficult to control and reduce the power consumption. This difficulty was caused from such a feature of the double-diffused MOS transistor that its channel length was defined by diffusion process and was difficult to be controlled.